CHARMM36 united atom chain model for lipids and surfactants

J Phys Chem B. 2014 Jan 16;118(2):547-56. doi: 10.1021/jp410344g. Epub 2014 Jan 6.

Abstract

Molecular simulations of lipids and surfactants require accurate parameters to reproduce and predict experimental properties. Previously, a united atom (UA) chain model was developed for the CHARMM27/27r lipids (Hénin, J., et al. J. Phys. Chem. B. 2008, 112, 7008-7015) but suffers from the flaw that bilayer simulations using the model require an imposed surface area ensemble, which limits its use to pure bilayer systems. A UA-chain model has been developed based on the CHARMM36 (C36) all-atom lipid parameters, termed C36-UA, and agreed well with bulk, lipid membrane, and micelle formation of a surfactant. Molecular dynamics (MD) simulations of alkanes (heptane and pentadecane) were used to test the validity of C36-UA on density, heat of vaporization, and liquid self-diffusion constants. Then, simulations using C36-UA resulted in accurate properties (surface area per lipid, X-ray and neutron form factors, and chain order parameters) of various saturated- and unsaturated-chain bilayers. When mixed with the all-atom cholesterol model and tested with a series of 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)/cholesterol mixtures, the C36-UA model performed well. Simulations of self-assembly of a surfactant (dodecylphosphocholine, DPC) using C36-UA suggest an aggregation number of 53 ± 11 DPC molecules at 0.45 M of DPC, which agrees well with experimental estimates. Therefore, the C36-UA force field offers a useful alternative to the all-atom C36 lipid force field by requiring less computational cost while still maintaining the same level of accuracy, which may prove useful for large systems with proteins.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Cholesterol / chemistry
  • Dimyristoylphosphatidylcholine / chemistry
  • Lipid Bilayers / chemistry
  • Lipids / chemistry*
  • Micelles
  • Molecular Dynamics Simulation*
  • Phosphorylcholine / analogs & derivatives
  • Phosphorylcholine / chemistry
  • Surface-Active Agents / chemistry*

Substances

  • Lipid Bilayers
  • Lipids
  • Micelles
  • Surface-Active Agents
  • Phosphorylcholine
  • dodecylphosphocholine
  • Cholesterol
  • Dimyristoylphosphatidylcholine